Snap-acting thermostat and bimetal blade therefor



H. F. MALONE Feb, 11, 1958 SNAP-ACTING THERMOSTAT AND BIMETAL BLADE THEREFOR Filed April 11, 1956 2 Sheets-Sheet 1 FIG.

INVENTOR Homer F. Malone h M ZMYy Z-I ATTORNEYS H. F. MALONE Feb. 11, 1958 SNAP-ACTING THERMOSTAT AND BIMETAL BLADE THEREFOR Filed April 11, 1956 2 Sheets-Sheet 2 INVENTOR Homer F. Malone United States Patent SNAP-ACTING THERMOSTAT AND BIMETAL BLADE THEREFOR Homer F. Malone, Millburn, N. J., assignor to The Wilcolater Company, Elizabeth, N. J., a corporation of Delaware Application April 11, 1956, Serial No. 577,607

18 Claims. (Cl. 200138) My invention relates to improvements in snap-acting thermostats including a novel bimetal snap-acting unit and blade therefor.

Bimetal blades are used in various types of thermostats, particularly where the thermostat can be mounted, so that it is responsive to the temperatures to be controlled. For the most part, these thermostats act gradually as the temperature changes and eventually move a movable contact away from a fixed contact of a switch. Some bimetal blades are snap acting, but in accordance with the present invention, the bimetal blade is not only snapacting but is adapted to apply increasing pressures to the contacts up until the point when the blade snaps.

Accordingly, the primary object of the invention is to provide an improved snap-acting blade unit whichis responsive to temperature changes and which applies a reacting force in one direction before it snaps from one stable position to another.

A further object of the invention'is to provide a snapacting bimetallic unit and switch mechanism actuated thereby.

In accordance with the invention, the improved snapacting unit includes a bimetal blade having a permanent concave deformation at one side or end supported with that end in fixed position on a mounting means, while the opposite side or end is free to move between two stable positions with a snap action.- Means is provided at the mounting end to apply a stress to the blade. The blade comprises a body section surrounding an integral tongue, one end of the tongue being integral with the movable end portion of the body of the blade. The blade is dished to one stable position on its high-expanding side, except for the tongue which normally extends in line with the surface of the movable end portion of the blade. The structure is such that the movable end of the tongue extends to one side of the body of the blade when the blade is in one of its stable positions and then to the other side of the body of the blade when the blade is snapped to its other stable position.

The snap-acting bimetal blade unit also advantageously includes means for adjusting the blade to snap at predetermined temperatures and a control means actuated by the movable end of the tongue.

When the snap-acting bimetal unit is used for actuating a control means such as a valve, a switch or for moving a movable electric contact with respect to a fixed contact, means is provided for connecting the movable end of the tongue with the control means. In this connection the arrangement is such that as the temperature of the blade rises, the tongue provides continuous pressures on the contacts or switch, for example, so that there is no chattering of the switch contacts. This pressure is maintained up to the point when the bimetal blade snaps and quickly moves the movable contact away from the fixed contact or throws the switch.

Illustrative embodiments of snap-acting thermostats and of a bimetal blade constructed in accordance with the inventionare shown in the accompanying drawings ice and described hereinafter in detail in connection therewith.

In the drawings:

Fig. 1 is an elevational view of a snap-acting thermostatic switch including a bimetal blade unit constructed according to the invention;

Fig. 2 is a vertical sectional view taken on the line 2-2 of Fig. 1;

Fig. 3 is a view of the snap-acting bimetal blade shown in Fig. 2;

Fig. 4 is a sectional view taken on the line 44 of Fig. 2;

Figs. 5 and 6 are sectional views taken on the line 5-5 of Fig. 3 showing the snap-acting bimetal blade in its two stable positions;

Fig. 7 is a vertical longitudinal sectional view of a space heater thermostatic switch including a modified form of bimetal blade unit; and

Fig. 8 is a broken view of the blade of Fig. 7.

While the snap-acting bimetallic unit of the present invention may be used in various types of thermostats, particularly for water heaters, room heaters, room coolers and other purposes, it is illustrated in Figs. 1 to 6 in connection with a thermostatic electric switch adapted to be strapped to a conventional domestic hot water tank and in Fig. 7 in connection with a room or space heater thermostat. Referring to Figs. 1 to 6 of the drawings, the thermostatic switch illustrated therein comprises an opensided sheet metal casing 10, in which the snap-acting bimetallic unit is mounted, and a casing 12 or switch housing of insulating material, such as Bakelite set on a sheet of insulating material 14 covering the outer surface of the casing 10, as shown in Fig. 2. The casing 12 is secured to the casing 10 by rivets 16. i

The outer portion of the metal casing 10 is pressed inwardly intermediate its ends to provide a plain oifset section 18 on which the bimetallic snap-acting unit is mounted, this unit comprising a snap-acting bimetal blade 20, a metal block 22 and a bowed spring metal plate 26. The blade 20 is welded at one end to the metal block 22 and this assembly, together with the spring plate 26, is fastened to the portion 18 of the casing 10 by a screw 24 extending therethrough. The bowed spring metal plate 26 is provided to limit or stiifen the crosswise deformation of the bimetal blade 20 when it snaps to the shape shown in Fig. 5, the plate 26 including end projections 27 respectively engaging the edge portions of the attachment end of the blade in the manner shown in Fig. 4.

In a preferred construction, the bimetal blade 20 is cut from a sheet of bimetallic material to the outline shape shown in Fig. 3. In this View the blade is shown as comprising a rounded end portion 28, and an opposite straigh -edged end portion and straight sides 30. In cutting the blade, a substantially U-shaped slot 32, an elongated oval-ended opening 34 and a slot 36 midway of the straight end are formed, the latter leaving end portions 38 extending toward each other from the ends of the sides 30. The cut-outs for the openings 32 and 34 leave a tongue 40 having legs 42, the ends of the legs 42 being integral with the curved end portion 23 of the blade 20. In cutting the blade, it has been found advantageous and convenient to leave a projection 44 at the end of the tongue 40 for mounting a movable contact or for connection to means for operating a movable contact or a switch or other control mechanism.

The bimetal sheet from which the blade is cut, is made up of two sheets, respectively, of high and low-expand- 3 ginning of the U-shaped slot, so that it is concave on its high-expanding side. The temperature range in which the blade is to operate governs the amount of dishing or bowing of the, blade. 7 After the cross-bowing operation has been completed to provide a shape approximating that shown in Fig. 4, the blade is stressed in avise provided with amicrometer screw. The blade is provided with notches 46, engaging pins of the vise. When a blade is in place betweeri the pins, the micrometer screw is operated to move the portions 38 toward each other to. stress the mounting end portions of the body of the blade toward each other to a predetermined extent.

The extent to which the body of the blade 20 is stressed in the vise determines the temperature differential or range through which the blade actuatm. For a room heater the bladeis stressed to actuate from one stable position to the other with a temperature ditferenti'al or range of about 1.5 F. For a water heater, the range need not be so narrow and may be from 8 to 15 F. 7

While the blade is held in the vise, the metal block 22 is positioned under the end portions 38 and spot welded thereto with two spot welds for each of the end portions 38, as shown in Fig. 3. The block 22 serves as a means for stressing the body ofthe blade while in operation and holding it in a predetermined stressed condition. This drawing in, of the ends of the sides St at the mounting end of the blade produces a longitudinal curvature in theside's when the blade is in its stable positions, as indicated ,in Figs. .2, and 6. The notches in the end portions 38-and the whole in'the block 22 line up so as to receivethe'mounting screw 24. I

In 'niounting the blade 21) in the casing 10, its highexpanding side is faced toward the back portion of the casing,'as shown in Figs. 2 and 4, while its low-expanding side faces toward the water tank wall oropen side of the casing 10. It is thus in position to be directly responsive to the heat of the hot water tank. v

. Means is provided in the casing for adjusting the blade 20, so that it will snap at a predetermined temperature. This means includesla rectangular-shaped frame 48 fitting inside the casing 10 and arranged so as not to appreciably cover the blade 20. This frame includes a projecting hook 50 pivoted in'a slot in the end of the casing ltl'adjacent the freeend of the blade 20. The back surfaces of the sides of the frame at the position of the mounting end of the blade include pressed-out projections 52 respectively bearing against the edge portions of the blade, as shown'in'Pjig. 4, The other end of the frame 48, asseen in 'Fig. 2,'cornprises a flanged end cross member54'provided with a central threaded opening receiving a temperature adjusting screw 56, which extends through the wall of the casing 10 and sheet 14 and carries a pointer or indicator 58 operable over a temperature scale 66 printed on the upper surface of the sheet 14. The indicator 58 is rotatable with the screw 56 to the extent of engaging a stop pin 62. As the indicator 58 is moved toward higher temperatures by turning the screw 56, the

frame 48 is pulled toward the casing 10 causing the projections 52 on the frame to change the position of the end portions 33 of the blade so as to offer increased opposition to thermal operation. When the sc1'ew'56 is rotated to move the indicator 58 toward the lower temperatures of the scale, the edges of the blade and the ends of thespring 26 follow the projections 52 to change the position so as to offer decreased opposition to thermal operation. When the temperature of the blade reaches the set temperature, it snaps from the position or condition shown in Figs. 2 and Sto thatshown in Fig. 6.

In the construction shown in the drawings, which is particularly adapted for controlling a hot water heater, the projection 44 of the tongue 40 extends into a transverse slot in one end portion of a reciprocable bar 64.

extending through openings in the part 18 of the casing 19, the sheet 14 and the wallet the casing 12. The slot in the casing 12 is shown at 66. The projection 44 is shown with a crimp to increase its efiective thickness to, fit the slot in the bar 64. In the casing 12 the bar 64 is provided with a transverse slot receiving the projecting erid of a flexible metal switch blade 68 fixed to an electrical terminal 79 extending through the wall of the casing 12 and provided with a connecting screw 72. The switch blade 63 carries a contact 74 engaging a fixed contact 76 carried by an electric terminal 78 provided with a connectingscrew 3th This structure provides a single pole, single throw switch for controlling the operation of the water heater, but it is to be understood that another blade and contacts may be provided to permit single pole double throw, or double pole single throw switching.

The thermostatic switch, as illustrated in Figs. 1, 2 and 4-is adapted to be mounted directly on the metal wall 82 of a hot water heating tank with the bimetal blade 21 facing directly toward the wall of the tank so that it is subjected to the temperature of the wall. The sides of the metal casing 10 are, therefore, provided with pressed-out hooks or lugs 34 to be engaged by a strap extending around the water tank or by other clamping means so that the thermostat is held against the tank. The thermostat, for example, may be mounted adjacent the top of the tank and connected up so that an electric heater in the upper portion of the tank is operated through an electric circuit, one side of which is connected into the terminals 79 and 73 by the connecting screws 72 and Sit, respectively.

Figs. 1 and 2 of the drawings show the indicator 58 set at a temperature of l30 F. and the movable contact 74 engaging the "fixed contact 76. The electric circuit is, therefore, closed as the water in the tank is being heated. As the water approaches the set temperature of F., the bimetal blade 20 is gradually heated up. During this operation, since the high-expanding side of the blade 26 expands more rapidly than the low-expanding side, the tongue 49, tends to be bowed so that it applies an increasing pressure on the bar 64 pressing the contact 74 more firmly against the fixed contact 76. This increase in pressure continues until the blade snaps from the position shown in Figs. 2 and 5 to the position shown in Fig. 6. in going through this change, the movable end or border portion 28 of the blade takes a reverse trans' verse curvature and mov es to the position shown in Fig. 6. Since the ends of the legs 42 of the tongue 40 are integral with the end border portion 28 of the blade, they normally extend approximately inline with the end portion 28, except for the curvature acquired through chan es in temperature, and when the blade snaps, the end 44 of the tongue 49 moves relative to the end portions 38 and at about right angles thereto to separate the movable contact 74 from the fixed contact 76, thereby opening the switch. The temperature of the bimetal blade 20 follow that of the tank, to which the thermostat is attached and snaps to the position shown in Fig. 2 when the tank and blade are cooled.

While the cross-sectional shape of the curved end portion of the blade or sheet of bimetal has been referred to as curved or dished, the end portions 38 are bent after welding so as toextend approximately in a straight incline away from the edges of the block 22, asshown in Fig. 4. Howeventhe sides 30 are not only dished and Warped on the'high-expanding sidein theposition shown in'Figs. Zand 5, but also curve gradually from the mounting end of the blade. The end border portion 28 is formed to a slight concave shape on its high-expanding side, the center of the concavity being toward the center of the opening 34. When the blade is snapped to the position shown in Fig. 6, the curvature and dishing of the body of the blade are reversed, except that the mounting end portions 38 of the blade still slope in the samedirection away from the edges of the block 22,

The spring member 26 is shaped and provided in back of the mounting end of the blade 20 in order to cause the blade arms '38 to rest against the projections 52 of the frame 48 as the frame is moved to diiferenttemperature settings.

The room or space heater thermostatic switch shown in Fig. 7 comprises a modified construction of the bimetallic blade unit, including a current-carrying bimetal blade20'. This blade, as shown in Fig. 8, includes a solid current-carrying tongue 40 and sides 30 extend substantially uniformly to the attachment end of the blade where their ends are biased toward each other and welded to a-sheet metal spring 84 which also serves the purposes and functions of the spring 26. The blade unit shown in Figs. 7 and 8 has essentially the same functions and preformed structures as the blade 20 but is particularly adapted for conducting electric current. The sheet metal spring 84 is preferably of suitable conducting spring metal and the end portions are bowed up, as viewed inFig. 8, toward the high-expanding side of the blade 20'.

In accordance with the showing in Fig. 7, the blade 20' is mounted in a thermostatic switch structure, which may include a casing, not shown, in which is secured a mounting block of insulating material 85 carrying elec* tric terminals 86 and 87 provided with terminal connector screws 88 and 89. A mounting screw bolt 90 extends through the terminal 87 and secures an assembly comprising a stop plate 91, the spring 84 of the blade 20' and a metal spacer block 92 similar to the block 22 but not welded to the bimetal blade. The bolt 90 holds the blade 20' in the position shown in Fig. 7 with the tongue 40'- provided with a contact 93 extending directly over a contact 94 carried by an adjusting screw 95 extending 0 through a rivet securing the terminal 86 to the mounting block 85.

.The extent of the movement of the tongue 40' is de termined by adjusting the position of the contact 94 and a limit screw 96 carried by the stop plate 91.

The temperature at which the bimetal blade 20 snaps to the off or on positions is set or controlled by a dial -97 having an indicator 98 movable over a temperature scale carried on a plate 99. The dial 97 is carried on a dial shaft 100 threaded in a plate 102, the end of the shafts100 having a bearing in a yoke 104 extending transversely of the attachment end of the blade in a manner similar to that of the part of the frame 48 shown in Fig. 4. The yoke 104 includes end projections 106 bearing against the edge portions of the sides 30 welded to the spring member 84. The spring member 84 is generally concave toward the yoke 104 and the sides 30' are twisted or turned to the extent of the bend in the spring. The operation of the dial 97 serves to move the yoke 104 toward and away from the attachment end of the blade20' to respectively decrease and increase the curvature in the attachment end of the blade, including the spring 84 to carry out functions described for the blade 20. The spring 84 may, if desired, be straight along the block 92 and bent at the edges of the block toward the yoke 94 so that the end portions of the spring 84 outwardly from the block 92 may be normally straight and extend at an angle toward the end portions of the yoke 104 carrying the projections 106. The dial stern 100 carries a stop 107 which may engage a part of the support for the plate 99 when in maximum and minimum positions.

One of the current leads for the space heater or for operating or controlling the space heater is connected into the terminals 86 and 87 and as long as the space is not up to the temperature set by the dial 97, the contact 93 will be in engagement with the contact-94 so that current flows through the bimetal blade from the bolt 90 via the spring 84, the sides 30 and the tongue 40 to the contact 93. Current is thereby supplied through the contact 94, adjusting screw 95 and terminal 86 to the current connection. When the space becomes heated to the set temperature, the bimetal blade 20' snaps from the dotted line position shown in Fig. 7 to the full line position to discontinue the supply of heat to the space.

When the temperature again falls, the blade snaps: to close the contacts 93 and 94. The sensitivity of the blade may be adjusted by adjusting the screws and 96. The screw 96 may be set so close that there will only be a few degrees difference between the opening and closing temperature of the switch.

Since the low expanding side of the bimetal blade 20 is toward the contact 94, increasing pressure will be applied by the tongue 40 as the temperature in the heated space rises, up to the point when the blade snaps to remove the contact 93. A thermostat similar to that shown in Fig. 7 may be used to control a room cooler, the tongue being actuated to open a normally closed control switch on a drop in room temperature to a pre-set point.

In making the snap acting bimetal blades for water heaters, room heaters and similar uses, they are preferably blanked out from bimetal sheet material having a thickness of approximately 0.15", or of somewhat thicker material. Blades constructed in accordance with the invention and now in use are approximately 1 and long and l and wide adjacent the movable end. The stressing means at the mounting end of the blade draws the sides toward each other by an appreciable amount so that the blade will be narrower at the mounting end than at the beginning of the tongue.

In the construction of Figs. 1 to 6, the tongue 40 is provided with relatively narrow legs 42 approximating in width in order to diminish the force with which snap action occurs. The tongue is formed at 44 in order to control its thickness at the place where it projects through the reciprocating bar 64, so that no lost motion occurs.

While the invention has been described and illustrated in connection with specific electric thermostatic switches, it will be understood that the improved bimetal blade and bimetal blade unit may be used for operating other types of switches or other mechanisms with a snap action in response to changes in temperature. Furthermore,

while the bimetallic blade or sheet is preferably formed and mounted in the manner described, it may be installed for certain purposes with the free end of the tongue fixed to a mounting and the adjacent border portion free to move relative thereto for actuating a contact, switch or mechanism.

I claim:

1. A snap-acting thermostat element comprising a sheet of bimetallic material having highand low-expanding faces and provided with a U-shaped slot spaced inwardly of the edge of the sheet and defining a tongue and a surrounding border, the end border portion of the sheet adjacent the free end or" the tongue being compressed in the plane of the sheet and at right angles to the sides of the U-shaped slot, the border area of the sheet alongside the tongue and adjacent the root end thereof being generally concave on the high-expanding face of said sheet at temperatures below an operating temperature, said border area of the sheet being generally concave on the low-expanding face of the sheet at temperatures above said operating temperature, said tongue being integral with and generally in the plane of the border area of the :sheet to which it is connected at its root, whereby the free end of the tongue and the border portion directly adjacent thereto move through a substantial distance relative to each other in a direction generally normal to the sheet when the temperature of the sheet changes from one side to the other of said operating temperature.

2. A thermostat element as claimed in claim 1, in which the border portion adjacent the free end of the tongue is provided with a slot generally parallel to the sides of the U-shaped slot, and means are provided for drawing the edges of the border slot toward each other whereby said end border portion is compressed.

3. A thermostat elcment as claimed in claim 2, in which the means for drawing comprises a metal piece connecting the parts of the end border portion on the opposites ide's of the border slot. 7

thermostat "element as claimed in claim 3, in which the --nietal piece is adjacent the high-expanding side ofthe sheetand is provided with a hole for mounting the thermostat element.

5, A thermostat element as claimed in claim 1, in which the tongue is p'rovidedwith an opening defining with the sides 'of the U-shaped slot spaced tongue legs.

6. A snap-acting electric thermostat comprising a thermostat element as claimed in claim 1, a casing, means for rigidly mounting the compressed end border portion in fixed relation to said casing, a first contact fixed with respect to said casing, and a second contact movable by said tongue into and out of engagement with said first contact.

7 A thermostat as claimed in claim 6, in which said casing has an open side, and said thermostat element is mountedin the casing with its lowexpanding face facing toward the open side of the casing.

8. A- thermostat as claimed in claim 7, including means carried by the casing for adjusting the snapping temperature of the bimetal sheet, said adjusting means including means engaging the opposite side edges of said end border portion for applying a bending stress thereto at about right angles to the face of the sheet.

, 9. A thermostat as claimed in claim 8, in which the adjusting means comprises a frame pivoted in the casing, portions of which respectively engage the opposite side edges of the said end border portion of the sheet on its low-expanding face, and means for pivoting the frame.-

10. A snap-acting electric thermostat including a casing, a snap-acting sheet of bimetallic material, mounted in said casing, said sheet having highand low-expanding faces and including a tongue having a free end spaced inwardly of the edge of the sheet, the sheet having a border substantially surrounding the tongue, the border portion extending beyond the free end of the tongue being divided and stressed in a gathering sense in a direction at right angles to the sides of the tongue, mounting means fixed to the divided border portion adjacent the free end of the tongue for securing the said stressed border portion in fixed position in the casing, the border areas of the sheet on the sides of the tongue and opposite to said border portion being generally concave on its high-expanding face up to the temperature at which the sheet straps on a rise in temperature, the border area of the sheet opposite said border portion being generally concave on its low-expanding face at temperatures above said temperature while the border portions along the sides of the tongue are twisted, the tongue being integral with and generally in line in an edgewise sense with the border area'of the sheet opposite that of the said border portion, whereby the free end of the tongue is movable relative'to the said border portion in a direction generally normal to'the sheet when the sheet snaps, a fixed contact, and arnovable contact co-operating with the fixed contact and movable out of engagement with the fixed contact by said free end of the tongue.

11. A thermostat as claimed in claim 10, in which the mounting meansis a spring extending across said border portion at right angles to the tongue.

, 12. A thermostat as claimed in claim 11, in which the spring is of sheet material secured to the high-expanding side of the sheet and concave on its face toward the sheet.

13. A snap-acting electric thermostat including a casing, a snap-acting sheet of bimetallic material mounted in said casing, said sheet having highand low-expanding faces and including a tongue having a free end spaced inwardly from the edge of the sheet, the sheet havinga border substantially surrounding the tongue, the border portions of the sheet extending beyond the free end of the tongue being spaced apart adjacent the free end of the tongue, a sheet spring overlying the parts ofthe end border: portions beyond the free end of the tongue and attachedthereto and holding said portions in stressed relation toward each other, said spring being biased ;to a curved shape, means for securing the stressed border portions .in fixed positionin the casing, the border areas of the sheet .on the sides of the tongue and opposite to' said border portion being generally concave on the highexpanding. face of the. sheet up to the temperature at which the sheet snaps on a rise in temperature, the border area of the sheet opposite said border portions being generally concave on the low-expanding face of the sheet at temperatures above said temperature while the border areas along the sides of the tongue are twisted, the tongue being integral with and generally in line in an edgewise sense with the border area of the sheet opposite said end border portions, whereby the free end of the tongue is movable relative to the said end border portions in a direction generally normal to the sheet when the sheet snaps, a fixed contact, and a movable contact cooperating with the fixed contact, and movable out of engagement with the fixed contact by the free end of the tongue.

. 14. An adjustable snap-acting thermostat comprisin a bimetal blade having high-expanding and low-expanding faces, and. being generally concave on one face at temperatures below an operating temperature, mounting means for rigidly securing one portion of said blade, and adjustable means including means engaging the said one face of the blade at spaced points for exerting pressure upon said one face in a direction generally normal to said one face, said'adjustable means being adapted to vary the concave shape of said blade adjacent said spaced points. 7

15. A thermostat as claimed in claim 14, characterized by said blade being mounted adjacent one end thereof by means engaging the said one end substantially centrally between the side edges of .the blade, and said adjustable means comprises means engaging the blade .ad-. jacent opposite side edge portions thereof and adjacent said one end thereof.

16. A thermostat as claimed in claim 15, in which a curved spring is mounted adjacent the said one end of the blade and engages the blade at spaced points generally opposite the points at which'said blade is engaged by said adjustable means, said spring tending to varythe concave shape of said blade in opposition to :said adjustable means.

17. A snap-acting thermostat comprising a bimetal blade having portions of generally concave shape on one face, mounting means for rigidly securing a limited portion of said blade, and adjustable mechanical means acting in a direction generally normal to said blade for varying the'concave shape of a limited portion thereof.

I18. A'thermostat'as claimed in claim 17, .in which. said adjustable mechanical means comprises a spring-and an adjustable member acting in opposition to said spring;

References Cited inthe file of this patent UNITED STATES PATENTS 2,266,537 Elmer Dec. 16, 1941 2,528,756 Kaser Nov. 7, 1950 2,701,830 Malone Feb. 8, 1955 2,707,216 Farison Apr. 26, 1955 

